This invention relates to telecommunications over packet networks, illustratively, the Internet, and more particularly, to a method and apparatus for enhancing Quality of Service (QoS) for voice communication over such a network.
Once information is injected into the Internet, its worldwide movement is free, and that constitutes a powerful motivator to the creation of Internet telephony. Consequently, numerous techniques and various offerings are now available for IP telephony (VoIP). Products such as CoolTalk (Netscape), Internet Connection Phone (IBM), IPhone (Intel), NetMeeting (Microsoft), Quarterdeck WebTalk (Quarterdeck), TeleVox (Voxware), WebPhone (Netspeak), etc. are examples thereof.
FIG. 1 presents a block diagram of a telephony adapter 10 that may used to couple a POTS (Plain Old Telephone Service) telephone to the Internet. Adapter 10 comprises a telephony port 2 that is connected to interface card 11, and a number of data ports that apply IP packets that are received from digital appliances, such as computers, to input terminals of switch 14. Interface card 11 emulates the central office environment by providing the necessary DC current, off-hook detection, ringing signal generation means, etc. The analog signal that is received at port 2 in the course of a conversation, i.e., following a detected off-hook state and prior to a detected on-hook state, is converted to digital form in A/D/A bi-directional converter module 12, and applied to D/IP/D (digital-to-IP, and IP-to-digital) bi-directional converter module 13. The IP packets of module 13 are applied to another input terminal of switch 14, which is a Layer 2 switch whose output is applied to controller 15. Controller 15 also manages switch 14.
Given that each port of switch 14 can be coupled to a source of packets, and that some of the packet sources are computers that may run applications that, themselves, output more than one stream of IP packets, it follows that the channel from telephony adapter 10 to ISP 111 (upstream channel of link 20) can be quite in demand. Typically, however, an ISP offers a relatively narrow bandwidth to upstream channels because, at least in the past, users tended to download a lot more information than they tended to upload. This fact, as well as the technical limitations of most commonly deployed residential high-speed data networks, has led most ISP providers to utilize an asymmetrical service, with a broader downstream bandwidth and a narrower upstream bandwidth (for example, asymmetrical DSL, also known as ADSL).
Since the notion of dedicated facilities as in the conventional telephone network does not exist in packet networks such as the Internet, IP telephony presents a challenge because the transmission facility between a user and the Internet is of limited bandwidth. This challenge is particularly acute in the upstream direction because of the smaller bandwidth provided by the ISP in that direction.